Cellular stress responses in the evolution of multicellular complexity

我们的研究项目解决了进化生物学中最具挑战性的课题之一--复杂性的进化。多细胞谱系中新的复杂性水平的出现取决于非生殖性(体细胞)细胞的进化。然而，尽管它意义重大，但在任何谱系中都不能很好地理解SOMA进化的机制基础。为了解决这一重要问题，我们使用了一组绿藻(Volvocales)，包括单细胞(例如衣藻)和多细胞物种(例如Volvox)，它们具有不同程度的复杂性。在Volvox carteri中，一个单一的基因--RegA--是决定体细胞命运的必要条件和充分条件。我们以前曾假设，SOMA的进化涉及允许单细胞有机体通过投资于生存来适应各种压力因素的途径的共同选择，但代价是立即繁殖。本研究的总体目标是阐明在多细胞进化过程中应激反应并入发育途径的机制基础。具体地说，我们想要解决RegA的发育调控可能是如何演变的。我们将追求几个相辅相成的目标和方法。(I)确定在环境胁迫期间与RegA诱导有关的信号转导途径的上游成分。(2)测试这些信号/途径是否也参与发育调节的REGA的诱导。(Iii)利用生物信息学和酵母单杂交系统确定负责RegA表达的调控元件(以探索预测的调控序列与其假定的结合因子之间的潜在相互作用)。这项拟议的研究提供了一个新的框架，基于预先存在的应激反应的共同选择，来解决体细胞和多细胞复杂性的进化。这项研究还涉及其他几个重要课题，包括顺式调控元件对形态特征进化的贡献，潜在的基因共选和功能多样化的机制(S)，以及细胞大小的差异如何转化为差异基因表达。

Our research program addresses one of the most challenging topics in evolutionary biology - the evolution of complexity. The emergence of new levels of complexity in multicellular lineages was contingent on the evolution of non-reproductive (somatic) cells. However, despite its significance, the mechanistic basis for the evolution of soma is not well understood in any lineage. To address this important question, we are using a group of green algae (the Volvocales) that comprises both unicellular (e.g, Chlamydomonas) and multicellular species (e.g., Volvox) with various levels of complexity. In Volvox carteri, a single gene - regA - is necessary and sufficient to establish the somatic cell fate. We have previously hypothesized that the evolution of soma involved the co-option of pathways that allow unicellular organisms to adaptively respond to various stress factors by investing in survival at a cost to immediate reproduction. The general objective of this research is to elucidate the mechanistic basis for the co-option of stress responses into developmental pathways during the evolution of multicellularity in Volvocales. Specifically, we want to address how the developmental regulation of regA might have evolved. We will pursue several complementary objectives and methodological approaches. (i) Identify upstream components of the signal transduction pathway associated with the induction of regA during environmental stress. (ii) Test if these signals/pathways are also involved in the developmentally-regulated induction of regA. (iii) Identify regulatory elements responsible for regA expression using bioinformatics and a yeast one-hybrid system (to probe for potential interactions between the predicted regulatory sequences and their postulated binding factors). The proposed research provides a new framework to address the evolution of soma and multicellular complexity based on the co-option of pre-existing responses to stress. This research also address several other important topics, including the contribution of cis-regulatory elements to the evolution of morphological traits, the mechanism(s) underlying gene co-option and functional diversification, and how differences in cell size translate into differential gene expression.********